This application is based on application Nos. 99-3027 and 99-62906 filed in the Korean Industrial Property Office on Jan. 30, 1999 and Dec. 27, 1999, respectively, the content of which are incorporated here into by reference.
(a) Field of the Invention
The present invention relates to an olefin polymerization process with the recycling of co-catalyst, particularly to a method of recycling co-catalyst for the activation of single-site pre-catalyst in the olefin polymerization. This invention, therefore, provides an olefin polymerization process that can reuse expensive co-catalyst for subsequent olefin polymerization so that the total amount of co-catalyst required can be significantly reduced.
(b) Description of the Related Art
In 1976, Professor Kaminsky of Germany reported that olefin polymerization could be accomplished by using zirconocendichloride compound as a catalyst with a methylaluminoxane (MAO) co-catalyst which was obtained through a partial hydrolysis of trimethylaluminum (A. Anderson, J. G. Corde. J. Herwing, W. Kaminsky, A. Merck, R. Mottweiler, J. Pein, H. Sinn, and H. J. Vollmer, Angew. Chem, Int. Ed. Engl. 15, 630 (1976)). MAO is conventionally called an aluminoxane because it is prepared by mixing trimethylaluminum with other alkyl aluminum. This single-site catalyst shows unique polymerization characteristics that can not be embodied by the conventional Ziegler-Natta catalysts. That is, molecular weight distribution of the produced polymer is narrow, co-polymerization is easy, and the co-monomer distribution is uniform. Furthermore, changes in catalyst ligands lead to variations in the molecular weight and degree of co-polymerization. Additionally, the stereoselectivity in the polymers can be changed according to the molecular symmetry of the catalysts. Therefore, a lot of attention has been drawn to the single-site catalysts due to these advantageous characteristics.
Compared to the Ziegler-Natta catalysts that have several independent active sites, the single-site catalysts have only one type of active site and are composed of various transition metals with suitable ligands. As described in detail below, transition metal metallocene compounds with one or two cyclopentadienyl ligands are the most representative examples, but non-metallocene type transition metal compounds with diimine ligands have also been studied recently (L. K. Johnson, C. K. Killian, M. Brookhart, J. Am. Chem. Soc., 117, 6414 (1995); L. K. Johnson, S. Mecking, M. Brookhart, J. Am. Chem. Soc., 118, 267 (1996); J. D. Scollard, D. H. McConville, N. C. Payne, J. J. Vittal, Macromol., 29, 5241 (1996); B. L. Small, M, Brookhart, A. M. A. Bennett, J. Am. Chem. Soc., 120, 4049 (1998); C. Wang, S. Friedrich, T. R. Younkin, R. T. Li, R. H. Grubbs. D. A. Bensleben, M. W. Day, Organometallics, 17, 3149 (1998)).
The metallocene type compounds of the above single-site pre-catalyst are described by the following General Formulae 1 or 2.
(C5R3m)pBs(C5R3m)MQ3xe2x88x92pxe2x80x83xe2x80x83[General Formula 1]

In the above General Formulae 1 and 2, M is a transition metal of Group 4, 5 (IVA, VA in the previous IUPAC form), or lanthanide series; (C5R3m) and (C5R3n) are a cyclopentadienyl, a substituted cyclopentadienyl ligand, or a substituted cyclopentadienyl ligand in which two adjacent carbon atoms of a C5 are joined together to form one or more C4-C16 rings by a hydrocarbyl radical, in which each R3, which can be the same as or different from other R3, is a hydrogen radical, or an alkyl, cycloalkyl, aryl, alkenyl, alkylaryl, arylalkyl, or arylalkenyl radical having from 1 to 20 carbon atoms, or a metalloid of Group 14 (IVB in the previous IUPAC form) substituted by hydrocarbyl radicals;
B is an alkylene carbon chain, alkenylene carbon chain having from 1 to 4 carbon atoms, arylene carbon chain, dialkyl germanium, dialkyl silicon, alkyl phosphine, or alkyl amine radical substituting on and bridging two cyclopentadienyl ligands, or a cyclopentadienyl ligand and JR4z-y ligands by a covalent bond;
R4 is a hydrogen radical, or an alkyl, aryl, alkenyl, alkylaryl, or arylalkyl radical having from 1 to 20 carbon atoms;
J is an element of Group 15 (VB in the previous IUPAC form) or Group 16 (VIB in the previous IUPAC form);
each Q, which can be the same as or different from other Q, is a halogen radical, an alkyl, alkenyl, aryl, alkylaryl, or arylalkyl radical having from 1 to 20 carbon atoms, or an alkylidene radical having from 1 to 20 carbon atoms;
L is a Lewis base;
s is 0 or 1 and p is 0, 1 or 2 provided that when p is 0, then s is 0, when s is 1, then
m is 4, and when s is 0, then m is 5;
z is a valence number of J provided that when J is an element of Group 15 (VB in the previous IUPAC form), then z is 3, and when J is an element of Group 16 (VIB in the previous IUPAC form), then z is 2;
x is 0 or 1 provided that when x is 0, then n is 5, y is 1, and w is greater than 0, and when x is 1, then n is 4, y is 2, and w is 0);
However, the single-site pre-catalyst itself described above does not have polymerizing activity. To activate this pre-catalyst, excess aluminoxane co-catalyst is required. In the polymerization process utilizing the single-site catalysts and co-catalysts, it takes hundreds to tens of thousands of moles of aluminum co-catalyst per each mole of single-site compounds in order to achieve commercially desired level of catalyst activity.
Excess aluminoxane remains in the polymer and deteriorates the physical properties of the resins. Furthermore, it obstructs the commercial applications of the catalyst system due to the increased price of the catalyst resulting from the high aluminoxane cost.
The polyolefin process can also be divided into solution, bulk, high pressure, slurry, and gas phase processes. Substituting conventional Ziegler-Natta catalysts with single-site catalysts has been applied to existing processes due to economic reasons. The greatest difficulty in the application of the single-site catalyst to the existing processes is the complete loss of the aluminoxane, which is not only costly but also used in large excess in each polymerization process.
Once a single-site catalyst and a co-catalyst are introduced in a polymerization reactor, the single-site catalyst and excess co-catalyst are discharged out of the polymerization reactor along with polymers and solutions (or monomers in a bulk process) at the end of a polymerization process resulting in a loss of catalyst activity. In other cases, in order to prevent problems in the post treatment process, various catalyst poisons are added to deactivate catalysts. Therefore, the single-site catalyst and co-catalyst are completely lost in each polymerization reaction. As described above, there are difficulties in commercializing single-site catalysts under existing technologies due to the high catalyst cost. Furthermore, the physical properties of resins deteriorate due to excessive quantities of aluminum residue in resins. Therefore, it would be preferable to develop single-site catalyst preparing technologies that not only decrease the amount of aluminoxane consumption, but also maintain effective activities in order for such single-site catalyst technologies to be commercialized at a lower cost.
The role of aluminoxane is to activate single-site pre-catalyst so that a cationic active species is formed, and to stabilize the corresponding cation as a counter anion. Furthermore, aluminoxane is also known to play a role as a scavenger, removing impurities during the polymerization. Therefore, the aluminoxane consumption can be greatly reduced if the excess aluminoxane is recycled except for that which is required to activate single-site pre-catalyst and to stabilize the active cationic species as a counter anion.
The inventors of this invention have also developed a related technology in which polymerization solution containing co-catalyst is recycled after separation of the produced polymer from the polymerization solution in a continuous slurry process (Korean Patent: 98-12659; PCT: PCT/KR99/00170). In this invention, polymerization is performed in a catalyst system in which metallocene catalyst is anchored on a support so that it does not go into solution and the co-catalyst is dissolved in a polymerization solution. After a polymerization reaction, the polymerization solution is separated from the polymers, and the co-catalyst dissolved in the solution is recycled in the continuous process so that the amount of co-catalyst is reduced. A diagram of the desired process is illustrated in FIG. 2 in order to provide a better understanding of the process.
However, the above technology, which necessitates separation of co-catalyst from the polymer after a polymerization, is applicable only to a slurry process and the polymerization media is limited to co-catalyst soluble solvents. Additionally, small amounts of leached catalyst from the support causes reactor fouling which disables the operation in a continuous process. Furthermore, the above technology still needs large amount of co-catalyst because the polymerization media is large excess to the catalyst and an optimum catalyst activity is achieved at a very high concentration ratio of co-catalyst to catalyst. In the above technology large amounts of co-catalyst are consumed by the reaction with impurities in the polymerization media and the co-catalyst physisorbed on polymers is also lost with the exposed polymers. Besides, a conventional olefin polymerization catalyst system employs a specific co-catalyst such as alkyl aluminum dissolved in a solvent, and the mixing or exchange of the co-catalyst is highly limited. Therefore, with the above technology, in order to switch to another catalyst/co-catalyst system, separation of the co-catalyst from the polymerization media or exchange of the whole polymerization media is necessary due to the restriction of the mixing or exchange of the catalyst or co-catalyst.
Considering the problems in the previous technology, development of new technology is necessary. It is desirable if the new technology is applicable to processes other than the slurry process and if it is also applicable regardless of the polymerization media. It is also desirable if reactor fouling can be prevented even in the event of the leaching of the supported catalyst, as well as if the amount of the co-catalyst can be reduced while the maximum ratio of the catalyst to co-catalyst for an optimal activity can be maintained. It is further desirable if the loss of the co-catalyst due to the impurities or during the polymerization process can be reduced and a low-cost common alkyl aluminum can be used as a scavenger substitute and the switching to a new process employing a new catalyst/co-catalyst system is convenient.
The purpose of this invention is to provide a method for an olefin polymerization with the recycling of co-catalyst such as aluminoxane, so that the amount of the co-catalyst for the activation of catalysts can be minimized and the loss of the co-catalyst by reactions with impurities or during the polymerization process can be greatly reduced. Furthermore, inexpensive common alkyl aluminum compounds can be used together with alumonoxane conveniently and the switching to another catalytic or co-catalytic system in the same process is easy using the same process. Additionally, the reactor fouling of the olefin polymerization process can be effectively prevented by recycling of co-catalyst during the activation step.
Another purpose of this invention is to provide a preparation method for an activated single-site catalyst which is applicable in a slurry or a gas phase process regardless of the polymerization media in the above olefin polymerization process. Particle size of the catalyst can be controlled by the changing the catalyst activation condition or the preliminary polymerization condition in this invention.
Still another purpose of the invention is to provide an olefin polymerization process using the activated catalyst prepared in the above method with the recycling of co-catalyst.